1. Field of the Invention
The present invention relates to a process of producing 2-(5-ethyl-5-hydroxymethyl-1,3-dioxane-2-yl)-2-methylpropane-1-ol (hereinafter referred to as “dioxane glycol” or “DOG”), which is represented by the following formula I:

2. Description of the Prior Art
DOG is produced, for example, by a process including the acetalization of hydroxypivalaldehyde (hereinafter referred to as “HPA”) represented by the following formula II:
with trimethylolpropane (hereinafter referred to as “TMP”) represented by the following formula III:
in the presence of an acid catalyst; the neutralization of the resultant reaction product liquid; and the filtration, washing and drying of the deposited DOG crystals (JP 62-59104B).
The acetalization under acidic condition is generally an equilibrium reaction, and DOG produced undergoes decomposition. Therefore, a solvent having a low solvent power to DOG such as water is generally used to deposit DOG as crystals immediately after its formation, thereby shifting the equilibrium toward the product side. Even when the solvent power to DOG is low, DOG dissolves in the solvent to some extent if a raw material such as TMP is dissolved in the solvent, thereby failing to prevent the decomposition of DOG. To reduce the amount of DOG dissolved in the mother liquor, the acetalization can be performed at lower temperatures or the solvent can be used in a large amount. However, these measures are industrially disadvantageous, because the acetalization becomes slow if the temperature is lowered and the use of a large amount of solvent requires great costs for the treatment of waste water.
In the production of DOG by a known method as disclosed in JP 62-59104B, the amount of waste water such as filtrates and washings after recovering DOG reaches about 10 times the amount of DOG produced. In addition, the yield is as low as 70 to 85 mol % and a considerable amount of the non-reacted raw materials and reaction intermediates remain in the reaction mother liquor after recovering the crystals. Therefore, the known method involves high environmental load in consideration of the treatment of waste water and waste products and the energy consumption.
DOG produced by a known method as disclosed in JP 62-59104B can be purified into a high purity DOG by recrystallization from an organic solvent. However, this is industrially disadvantageous because the number of steps for the production of DOG is significantly increased.
To reduce the amount of waste water and improve the yield, the filtrate can be reused in the next run of reaction. However, in a production method including a step of neutralizing the reaction product liquid with alkali after the reaction, a large amount of the acid catalyst is needed in the next run of reaction and the slats formed by the neutralization accumulate in the mother liquor during repeated reuse.
DOG crystals can be obtained by filtration directly after the reaction without neutralization with alkali, and the subsequent washing with water and drying. However, DOG produced by a known method decomposes upon heating for the production of polymer materials, etc., to deteriorate the properties of the product being produced.
In addition, the particle size of DOG produced by a known method as disclosed in JP 62-59104B is extremely small to make the handling thereof difficult.
DOG has the following two isomers: trans isomer and cis isomer.
DOG or its derivative having a high content of the trans isomer (hereinafter referred to as “high trans-isomer purity” or merely “high purity”) is preferably used as the raw material for industrial production. However, DOG produced by a known method contains a considerable amount of the cis isomer.
Known documents relating to the production of DOG are completely silent about the trans-isomer purity of DOG. As a result of extensive studies by the inventors, it has been found that DOG produced by known methods has a low trans-isomer purity, although mainly composed of the trans isomer. For example, the highest melting point of DOGs actually disclosed in the working examples of JP 62-59104B is 121.5° C. However, a purified DOG having a trans-isomer purity of 99% or more, which is obtained by the recrystallization from acetone of DOG having such highest melting point, shows a melting point of 125° C. or higher. The term “trans-isomer purity” referred to herein is the proportion (% by weight) of the trans isomer to the total weight of DOG.